wp_maybe_generate_attachment_metadata() WordPress Function

function wp_maybe_generate_attachment_metadata( $attachment ) {
	if ( empty( $attachment ) || empty( $attachment->ID ) ) {
		return;
	}

	$attachment_id = (int) $attachment->ID;
	$file          = get_attached_file( $attachment_id );
	$meta          = wp_get_attachment_metadata( $attachment_id );

	if ( empty( $meta ) && file_exists( $file ) ) {
		$_meta = get_post_meta( $attachment_id );
		$_lock = 'wp_generating_att_' . $attachment_id;

		if ( ! array_key_exists( '_wp_attachment_metadata', $_meta ) && ! get_transient( $_lock ) ) {
			set_transient( $_lock, $file );
			wp_update_attachment_metadata( $attachment_id, wp_generate_attachment_metadata( $attachment_id, $file ) );
			delete_transient( $_lock );
		}
	}
}
Uses	Description
wp-admin/includes/image.php:wp_generate_attachment_metadata()	Generate attachment meta data and create image sub-sizes for images.
wp-includes/option.php:get_transient()	Retrieves the value of a transient.
wp-includes/option.php:set_transient()	Sets/updates the value of a transient.
wp-includes/option.php:delete_transient()	Deletes a transient.
wp-includes/post.php:wp_get_attachment_metadata()	Retrieves attachment metadata for attachment ID.
wp-includes/post.php:wp_update_attachment_metadata()	Updates metadata for an attachment.
wp-includes/post.php:get_post_meta()	Retrieves a post meta field for the given post ID.
wp-includes/post.php:get_attached_file()	Retrieve attached file path based on attachment ID.